1. Field of the Invention
The present invention is directed to a safety ski binding adapted to maintain the front of a ski boot on the ski.
2. Description of Background Information
Safety bindings of the type according to the present invention are known as "front abutments" and generally comprise a body containing an energization mechanism acting on a retention jaw mounted in the rear part of the body of the front abutment. In certain front abutments, the jaw includes independent wings for lateral retention of the ski boot which are respectively journalled on the body about independent axes, and which are symmetrically arranged with respect to the vertical and longitudinal plane of symmetry of the front abutment. These lateral retention wings are elastically biased by the energization mechanism in the direction of the plane of symmetry of the front abutment so as to grip the front of the boot between the wings.
Such front abutments are described, for example, in French Patent No. 2,210,422 and Swiss Patent No. 509,810. These patents show the use of rollers to support the boot on the jaw that is formed by two journalled wings. More particularly, in the constructions of the front abutments described in these two patents, each lateral retention wing supports two rollers, that is, a lateral roller with a small diameter which is mounted for rotation about an axis at the rear end of the wing, which serves as support for the sole of the boot in the lateral direction, and a central roller of greater diameter than the lateral roller, which is mounted for rotation on an intermediate part of the arm of the wing between the rear end thereof and its journal axis, and which is closer to the plane of symmetry of the front abutment than the extreme lateral roller, and serves as support for the front of the sole in the longitudinal direction.
With such a construction, the large diameter central roller which operates to oppose the longitudinal forces has the disadvantage of "marking" the sole of the boot, since it digs into the material of the sole. This inhibits disengagement during the lateral release of the boot. This disadvantage cannot be eliminated by considerably increasing the radius of curvature of the central roller because the binding would become too bulky.
Another disadvantage of central large diameter rollers which sustain longitudinal forces, is that they have a trajectory imposed by the rotation of the wing about its axis during a lateral release of the front abutment, particularly because the rotation axis of each of these rollers is offset in the direction of the plane of symmetry of the front abutment with respect to the supporting arm of the lateral retention wing. Thus, it is not possible for the contact zone of the central roller to have a predetermined trajectory on the sole during lateral release. Yet, this is significant because the trajectory of the central roller determines the longitudinal movement of the boot in at least one direction during skiing. In fact, the rear binding exerts a thrust on the boot directed towards the front and to this thrust, which is substantially constant, are added occasional thrusts which are due to the flexion of the ski during skiing. Longitudinal thrusts of 200 daN (decanewtons) can be attained in extreme positions. The trajectory of each central roller thus determines the longitudinal engagement of the boot in the jaw (longitudinal movement towards the front connected to the lateral movement towards the exterior of the ski), or even its disengagement (longitudinal movement towards the rear connected to the lateral movement towards the exterior of the ski), or neutral behavior (no longitudinal movement).
Another disadvantage of central rollers is that their functioning deteriorates with wear and tear of the sole. In effect, when the front of the sole is hollowed by grooves or has contours due to wear and tear and repetitive shocks that the boot has endured, the roller catches on these different contours in the sole when the boot moves laterally, which hinders its disengagement. Moreover, to be efficient, each central roller must bear on a relatively hard surface since it has a relatively small diameter. Thus, if the sole of the boot is made of relatively flexible and deformable material, such as with a cross-country ski shoe or boot, the roller has a tendency to sink into the sole, which naturally hinders any lateral movement of the sole. This disadvantage also exists for soles which have a stiff upper part at the front and a layer of flexible material underneath to facilitate walking. In this case, the stiff part has a tendency to wear out more quickly than the flexible layer. As a result, the flexible layer projects from the side and the previously mentioned disadvantage is encountered again with soles of deformable material.
A front abutment as described above has another disadvantage concerning its method of construction. In effect, the central rollers have their own rotation axes which are independent from those of the lateral retention wings and it is thus necessary to provide an axis for each central roller, in addition to the axis of each wing, along with bearings for this axis and all the required secondary elements. This considerably increases the complexity of the binding and its cost.